It's costing me a boatload to properly boost Jean Grey, but it'll be worth it. I'll have a "perfect" Jean, so to speak. When you fuse, if you fuse two cards that are max level, it gives you a much bigger stats increase on the new card, whereas it only gives you a minimal increase otherwise. As a result, I've put a lot of money into maxing out each of the Jean's before fusing them so that I'll have a wrecking machine of a card in the end. Should be around 6k atk and 6k def after the mastery boost, to go along with her amazing ability.

Basically:

Lvl 1 3-Star Jean Grey without max mastery is 1060 atk and 1060 defense. Fuse two of those together and you get a card with 1272 atk and 1272 def as a base.

On the other hand, if you boost her up to Lvl 20 and max out her 20 Mastery, she'll have 3036 atk and 3036 def. Take two of those and fuse them together and the card you get will have 1880 atk and 1880 defense as a base.

So yea, if you have two copies of a card that you plan on fusing and then using in your deck, max both versions out (level and mastery) before fusing, and you'll in up with a much better card as a result.

I have a 2nd copy of that 3* Daredevil that im currently working on boosting to max level. When I get him there, THEN i'll fuse them to get the 4* Daredevil, and he'll end up much better in the end because of it.

Also, use this site as a reference. It has the stats of a lot of cards, plus base information on things like special combos you gain from paring two cards together in the same deck.

Gives my a total of 7373. I get special bonuses for Wolverine & Punisher being in the same team (merciless).

I have some cards that could make for a good start to a Speed deck (I can fuse Storm into a 4* and also have Human Torch and Nova who all provide huge bonuses to Speed cards). It's really hard to get away from Wolverine, though. He's so ******* good for 7 power.

Gives my a total of 7373. I get special bonuses for Wolverine & Punisher being in the same team (merciless).

I have some cards that could make for a good start to a Speed deck (I can fuse Storm into a 4* and also have Human Torch and Nova who all provide huge bonuses to Speed cards). It's really hard to get away from Wolverine, though. He's so ******* good for 7 power.

You can have a speed deck while still running Wolverine. Really, I dont know that id recommend a deck full of the same type, as it would get consistently destroyed by the type that its weak against. For instance, if you have all speed cards, youre going to have a LOT of fun against Tactic decks (best defensive decks + strong against speed). I think its best in the end to have 1 or 2 of a different type in there. Don't take that as gospel though, I might be completely wrong!

Max level/xp gives you the bonus. BUT, max mastery gives you better stats so that the bonus is bigger (because the bonus is a % of the fusing cards' atk/def, and you get a sizable atk/def boost when you hit max mastery level). So it's best to get both up to the highest possible level.